A recent international study led by the University of Michigan has revealed that fruits and vegetables grown in urban farms and gardens have a carbon footprint that is, on average, six times greater than conventionally grown produce. The research, which is the largest published study to compare the carbon footprints of urban and conventional agriculture, highlights the need to explore sustainable practices within the rapidly growing field of urban agriculture.

Urban agriculture, the practice of farming within cities, has gained popularity worldwide as a means to create sustainable urban food systems. However, despite its social and nutritional benefits, the carbon footprint of urban agriculture remains understudied. Most previous studies have focused on high-tech, energy-intensive forms of urban agriculture, such as vertical farms and rooftop greenhouses, which are not representative of the majority of urban farms.

In this study, researchers examined the carbon footprints of food produced at low-tech urban agriculture sites, including urban farms, individual gardens, and collective gardens. The study analyzed data from 73 urban farms and gardens in five countries, assessing greenhouse gas emissions associated with on-farm materials and activities over the farms' lifetimes. The emissions were then compared to those of conventionally grown crops.

The findings revealed that, on average, food produced through urban agriculture emitted 0.42 kilograms of carbon dioxide equivalents per serving, which is six times higher than the 0.07 kg CO2e per serving of conventionally grown produce. However, the study also identified some exceptions, where certain city-grown crops performed as well as or better than conventional agriculture under specific conditions. For example, tomatoes grown in soil on open-air urban plots had a lower carbon intensity than those grown in conventional greenhouses. Additionally, the emissions difference between conventional and urban agriculture disappeared for air-freighted crops such as asparagus.

The researchers emphasized the importance of making changes in site design and management to reduce the climate impact of urban agriculture. Cultivating crops that are typically greenhouse-grown or air-freighted can contribute to lowering carbon emissions. Furthermore, ensuring that urban agriculture maximizes social benefits, such as improving mental health, diet, and social networks, can make it more competitive against conventional agriculture when considering holistic benefits.

The study's co-lead author, Jason Hawes, highlighted the significance of urban agriculture as a feature of future sustainable cities but stressed the need to focus on reducing its climate impacts. By extending the lifetimes of infrastructure, utilizing urban waste as inputs, and generating high levels of social benefits, low-tech urban agriculture can become more carbon-competitive with conventional agriculture.

The study, published in the journal Nature Cities, involved collaboration with researchers from universities in Canada, France, Germany, Poland, and the United Kingdom, with ten collaborators co-authoring the study.

As urban agriculture continues to grow, addressing its carbon footprint is crucial for ensuring a sustainable and greener future for urban food production and the communities it serves.